Malignant solitary fibrous tumor of the orbit: Spectrum of histologic features

PURPOSE: Primary malignant solitary fibrous tumor (SFT) of the orbit is a rare spindle cell neoplasm that requires excisional biopsy for histopathological diagnosis. We present a clinical case using contemporary immunohistochemical stains, report on the latest World Health Organization classification, and provide a review of the literature. OBSERVATIONS: Report of a single case of a 65 year old male who presented with right-sided proptosis, limited adduction, ptosis, lateral globe displacement, and cheek festooning. Neuroimaging revealed a 2.2 cm, extraconal heterogeneous mass that diffusely enhanced. En-bloc tumor resection confirmed SFT malignancy based upon nuclear atypia, hypercellularity, and increased mitotic activity (13 mitotic figures/10 high powered fields). Ki-67 showed 2% nuclear staining in the benign tumor and 10–15% staining in the malignant counterpart. Immunohistochemical analysis revealed diffuse Stat6 positivity, CD 34 positivity with partial lack of staining within the malignant portion, S-100 positivity in the malignant portion, and overall negativity for CAM 5.2, desmin, actin, CD 31, and CD 117. CONCLUSIONS AND IMPORTANCE: Immunoprofiling is helpful to making the diagnosis of malignant solitary fibrous tumor of the orbit. Complete tumor resection continues to be the preferred treatment. The behavior of extrathoracic SFT is unpredictable, and patients with SFT in all locations require careful, long-term follow-up.